---Hello, this is Mike. Is Dr. Li in?---Sorry, he_________ to the west of Africa to help the patients there.A.has been B. is going C. has gone
Smoking is bad for your health. You should.
Aron water five days later.
This is______difficult problem that few students can work it out.
.He lives_______in the______village, but he is never_______.
Pollution is a serious problem. Scientists have _______ some good ways to save it.